Have you tried an epsom salt treatment yet? 1 tsp epsom salt per gallon for two days, then 2 tsp epsom salt per gallon for eight days, doing 100% daily water changes throughout treatment. You can find epsom salt at the pharmacy, it shouldn't cost too much.

Salt doesn't evaporate, so the only way to get rid of it is to do water changes. If you do less than 100% then you will be adding more salt water to already salted water, giving you a higher concentration of salt than you need. The 100% daily changes will ensure that every day he has the right amount of salt. Sorry if that doesn't make sense, I'm having a hard time describing it... :p

Salt doesn't evaporate, so the only way to get rid of it is to do water changes. If you do less than 100% then you will be adding more salt water to already salted water, giving you a higher concentration of salt than you need. The 100% daily changes will ensure that every day he has the right amount of salt. Sorry if that doesn't make sense, I'm having a hard time describing it... :p

Does that mean I have to pretty much dump him into a new environment every time?